In modern, urban communities, there are large areas of paved surfaces. These can be found on ordinary roads, major highways, parking lots, airport runways and elsewhere. This poses a problem of keeping such surfaces clean of dirt and debris. In colder climates, there is a problem of maintaining them free of snow and ice.
For many roads and highways, natural flow of traffic ensures that no major items of debris can build up. Additionally, wind and rain have a naturally cleaning action and remove smaller dust particles and the like. For streets in built up urban areas, accumulation of litter can be a problem.
Cleaning of litter is often addressed by providing motorized vehicles with a variety of powered brushes. Commonly, there is one main brush, and then at least one additional auxiliary brush specifically adapted to clean the portion of the road surface adjacent the curb, where litter and debris tend to collect. Such vehicles rely primarily on a brushing action, although there are proposals in the art to provide vacuum assistance and sometimes washing with water is provided. As such, to ensure good cleaning, an aggressive brushing action is provided by rotating brushes at a relatively high speed and maintaining the brushes pressed against these surfaces with a relatively high force. While this can be effective in cleaning a surface, it leads to a high power requirement and rapid wear of the brushes.
A related problem is clearing ice and snow, which can be a problem on any exterior car paved surface. A continuous sheet of ice presents an almost intractable problem, and usually can only readily be dealt with by application of salt or other materials to cause the ice to melt. For snow, or ice that is in powdery or loose form, there is the possibility of removing this mechanically.
For ordinary roads, snow plows, or snow blowers are commonly used for snow, or ice pellet accumulations, of any significant magnitude. For roads, this more than adequately cleans the road, although usually a thin layer of snow or ice pellets is left, often slightly compacted. Ordinary road vehicles can readily deal with such a thin layer of snow or ice and obtain adequate traction.
Airport runways present different problems. Firstly, aircraft travel at far greater speeds than ordinary motorized vehicles, yet usually are fitted with tires that provide worse traction capabilities. Consequently, any significant accumulation of snow or ice can cause considerable difficulties for aircraft landing and taking off. This can result in poor braking ability of an aircraft, skidding, loosing control and leaving runways.
An additional problem is provided by aircraft engines. Ordinary aircraft engines, such as jet engines, are extremely powerful, and require vast quantities of air. As such, a jet engine and the like, can create a strong suction at its inlet, and correspondingly produce a very strong jet at the outlet.
For takeoff, when an aircraft's engines are typically open to full throttle, this presents the possibility of debris on runways being sucked into the engines, possibly damaging the engines. Similarly, the jet at the outlet of the engine can pick up debris from the ground and cause it to be thrown large distances. Such debris can possibly impact vehicles, other aircraft or bystanders causing injury or damage.
For all these reasons, it is highly desirable to maintain airport runways in as clean a condition as possible. Conventional runway sweepers typically comprise a large cylindrical brush mounted at the front end of a truck or the like. The truck is run up and down the runway in various patterns, for the removal of dirt, debris, snow or whatever material is present. This again presents the same problems as conventional road sweepers, as typically the brush is rotated at a fairly fast rate with the intention of throwing swept materials some distance and discouraging material from clinging to the bristles of the rotating broom or brush.
Even so, it has been recognized that one of the problems of the simple cylindrical brush is that some pieces of debris or other material may cling to the brush for a short time and then fall down behind the brush. A proposed solution to this is to provide some sort of air duct along the back of the brush to blow away this debris. Nonetheless, the main cleaning effect is still provided by the brush, and as for conventional road sweepers, there is a problem of providing power to rotate the brush at a reasonable speed and relatively rapid wear rate of the brush.
U.S. patents in this art that disclose cleaning or sweeping arrangements, known to the applicant are:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,189,932 B. Daneman 3,222,706 K. B. Kaar et al 5,249,332 Wilkerson 1,211,902 F. L. Warner 4,773,121 Young 3,676,891 Murray et al 3,241,173 C. O. Finn ______________________________________
A number of these patents show arrangements provided with brushes combined with some sort of vacuum assistance. Thus the Daneman, Kaar et al, and Wilkerson patents all disclose arrangements which have some combination of brushes and a vacuum arrangement. A common characteristic of these arrangements is that the airflow is always used in a suction mode.
The Warner and Young patents are of some similarity, and they both show some sort of pickup device in which air is directed at a surface and a corresponding suction duct is provided. Again, the basis intention is removal of dirt or debris by a suction effect.
A vacuum machine for street cleaning is disclosed in the Murray et al patent, which provides flinger blades, intended to encourage air to flow under leaves or debris, so that they can be removed by suction.
The Finn patent discloses a so-called multi-purpose device, although it is primarily intended for use in seeding, fertilizing and like agricultural applications. One configuration is shown in which it is arranged to provide a horizontal air blast, e.g. for use as a wind drawing device. However, this is independent of any brushing arrangement.
Another known proposal provides an air blast behind a rotating brush. The intention is to clear away any debris that may fall off the back of the brush. The common arrangement is to provide a fairly modest airflow, of the order of 6-9,000 cfm. To achieve adequate velocity, this is then passed through a small outlet with a diameter of 4-6 inches. While the velocity at the outlet may be adequate, this produces a jet or blast that is too small to be adequate and which dissipates too quickly. This has not proven effective in removing debris that falls down behind a brush, so that commonly two or more passes must be made to achieve adequate cleaning or brushing of a surface.